1. Field of the Invention
The present invention generally relates to automobiles and, more specifically, to automobile differential gears.
2. Description of the Related Art
Generally, vehicles include a gear system to transmit rotational power from an engine to driven wheels. When a vehicle turns a corner, the driven wheels of the vehicle travel paths of different lengths, i.e., the wheel on the inside of the curve travels a shorter distance than the wheel on the outside of the curve. Thus, there is a need to provide different rotational speeds to the driven wheels in such an instance.
Typically, a vehicle employs a differential gear to allow the driven wheels of the vehicle to be driven at different rotational speeds. Referring to FIG. 1, a vehicle 1 includes an engine 10, wheels 20a-20d, a transmission 30, a differential gear 40, and wheel shafts 50a, 50b. The illustrated vehicle 1 is of a front wheel drive type, and thus the two front wheels 20a, 20b are driven. The transmission 30 transmits rotational power from the engine 10 to the driven wheels 20a, 20b via the differential gear 40 and the wheel shafts 50a, 50b. While the vehicle 1 is moving straight ahead, the differential gear 40 rotates the wheel shafts 50a, 50b at substantially the same speed. On the other hand, the differential gear 40 rotates the wheel shafts 50a, 50b at different speeds when the vehicle 1 turns a corner. The differential gear 40 is configured to accelerate the rotational speed of the wheel on the outside of the curve while decelerating the rotational speed of the wheel on the inside of the curve by an equal and opposite amount relative to the average rotational speed of the drive-line.
Even while traveling straight ahead, a vehicle may encounter a situation in which the driven wheels do not rotate at substantially the same speed. Such a situation typically occurs when the driven wheels experience different road surface conditions. For example, if one of the driven wheels is on an icy surface while the other is not, the wheel on the icy surface would overspin while reducing the rotational speed of the other wheel via the differential gear. Because the maximum transmitted torque of either axle shaft is limited by the maximum supported or sustained torque of the opposite axle shaft, the effect is that the torque on the well supported axle shaft decreases as the rotational speed of that axle shaft decreases. This effect manifests itself in situations which may result in a decrease in torque supplied to the other wheel. Thus, there is a need to provide a differential gear which can effectively provide torque to the well supported driven axle attached to the wheel that experiences high resistive loads (e.g. those with high coefficients of relative friction between the tire and road surface) when the set of driven wheels experience different road surface conditions.